JP7125342B2 - Aqueous dispersion of precipitated calcium carbonate - Google Patents

Description

The present invention relates to dispersion coatings. In particular, the present invention relates to dispersion coating compositions suitable for obtaining barrier properties on substrates, as well as methods of making such compositions and their uses.

Polyethylene (PE), waxes, and fluorocarbons are still commonly used barrier materials in paper and cardboard products. However, environmentally friendly barrier solutions are becoming more environmentally attractive in the packaging industry. In particular, there is a demand for products that do not contain fossil-based barrier materials. Current market forecasts estimate that water based barrier coating (WBBC) products will primarily reduce waxes and fluorocarbons to gain market share, but WBBC coatings will also replace PE plastic materials. A WBBC coating composition typically comprises an aqueous polymer dispersion and a platelet mineral such as talc (see, eg, US Pat. No. 5,400,000). Such materials are capable of creating an intricate network of particles within the coating structure, and these network of particles enhance barrier properties primarily obtained by applying a binder film on the substrate surface.

Various combinations of talc and ground calcium carbonate are disclosed in US Pat.

Talcum, or "talc" for short, is a substance that is difficult to disperse in water. Furthermore, the talc platelets move and form clumps, which means that most of the added talc does not contribute to barrier properties. FIG. 1 shows a typical talc coating on a substrate densely packed with particles.

International Publication No. 2008/141771 U.S. Patent Application Publication No. 2011237730 International Publication No. 2008/096274 International Publication No. 2014/202836

SUMMARY OF THE INVENTION The present invention seeks to solve at least some of the problems associated with the art and to provide novel mineral pigment compositions suitable for providing dispersed barrier coatings on substrates.

The present invention is a coating composition in which talc is dispersed with calcium carbonate particles to form a stable dispersion into which a binder and optionally other ingredients can be incorporated and which can be used to apply a dispersed coating on a substrate. based on the idea of forming

Surprisingly, calcium carbonate particles are provided in the form of precipitated calcium carbonate particles having a narrow size distribution and an average particle size in the nanometer range, and the particles and platelet-like particles are combined in water or an aqueous solution. It has been found that talc can be effectively dispersed in an aqueous medium when mixed in a weight ratio of, for example, about 1:10 up to 1:1, especially a weight ratio of 1:5 to 1:3.

The compositions thus obtained can be combined with water and optionally with a carrier medium known per se to provide coating compositions suitable for dispersion coating of substrates such as paper and cardboard. can.

More specifically, the aqueous dispersions of the invention are characterized primarily by what is stated in the characterizing part of claim 1 .

The method of the invention is characterized by what is stated in the characterizing part of claim 16 .

The uses are characterized by what is stated in claims 22-27 and the coating compositions of the invention are characterized by what is stated in the characterizing part of claim 28.

The invention provides many advantages. Thus, stable dispersions are readily obtained, the shelf life of which exceeds one month, typically two months.

In addition, the coating composition has a high solids (dry matter) content, which can facilitate removal of water after coating.

Precipitated calcium carbonate (PCC) particles with average diameters in the nanometer range have been found to act effectively as thickeners in dispersions and provide excellent coating properties. Conventional thickeners can be reduced in amount or eliminated entirely. Such thickeners are known to impair the barrier properties of dispersion coatings.

The dispersion coatings of the present invention have improved gas and mineral oil barrier properties and are particularly suitable for making materials for containing and packaging food products.

The present technology will now be discussed in more detail by way of example embodiments and with reference to the accompanying drawings.

FIG. 2 is a scanning micrograph (hereinafter also referred to as “SEM”) of a reference talc dispersion showing loading of talc particles. FIG. 4 shows a scanning micrograph of a reference talc dispersion showing loading of talc particles. FIG. 4 shows a scanning micrograph of a reference talc dispersion showing loading of talc particles. FIG. 12 shows a corresponding SEM of a dispersion in accordance with embodiments of the present technology; FIG. 12 shows a corresponding SEM of a dispersion in accordance with embodiments of the present technology; FIG. 12 shows a corresponding SEM of a dispersion in accordance with embodiments of the present technology; FIG. 3 shows an SEM of one pure nano-PCC product used in the present invention;

As noted above, in one embodiment, the present technology involves providing a stable aqueous dispersion of platelet-shaped particles and precipitated calcium carbonate. This dispersion is typically
- 50 to 95 parts by weight of platelet-shaped particles;
- 5-50 parts by weight of precipitated calcium carbonate particles with an average diameter of 30-60 nm.

The term "stable" as used in relation to the dispersions of the present invention typically means less than 5% by weight, preferably less than 1% by weight of It indicates that suspended solids settle.

In one embodiment, the dispersion has a dry matter content of more than 30%, in particular 40-60% by weight of the dispersion. The viscosity (Brookfield viscosity at 100 rpm) is typically 200-5000 cP, preferably 300-2500 cP, such as 400-2500 cP, especially about 500-2000 cP, such as about 1000-2000 cP.

In one embodiment, the dispersion comprises 60-85 parts by weight, especially 70-80 parts by weight of platelet-shaped particles and 15-40 parts by weight, especially 18-28 parts by weight of precipitated calcium carbonate particles.

The platelet-shaped particles can be selected from the group of talc, kaolin, bentonite and combinations thereof, but talc and mixtures of talc and other particles are particularly preferred.

The talc used typically has a particle size (Sedigraph particle size) of less than 50 μm. In one embodiment, the talc has a median particle size (d50) of about 1-10 μm. The proportion of particles smaller than 2 μm is, for example, about 10-60% by weight.

A suitable dispersion comprises 50 to 95 parts by weight of platelet-shaped particles, such as talc, dispersed in a high shear zone with 5 to 50 parts by weight of precipitated calcium carbonate particles having an average particle size of 30 to 60 μm in an aqueous phase. can be obtained by

In one preferred embodiment, the aqueous phase comprises an aqueous slurry or dispersion of precipitated calcium carbonate particles of average diameter 30-60 nm in water.

In the present invention, PCC particles are characterized by having a "diameter" of 30-60 nm. This is not an affirmative indication that all particles are spherical, although at least a substantial portion of all particles will generally meet the definition for spherical particles. Broadly, the term "diameter" indicates that the particles have an average size in the indicated range. The smallest diameter is typically 20 nm.

Suitable PCC particles can be produced, for example, as disclosed in US Pat. The particle size of the PCC particles is given as the Sedigraph particle size. Particle size can also be confirmed, for example, from SEM images of pure nano-PCC products and can be evaluated and determined. In this regard, see the SEM of Figure 7, which shows the particles of this product. Particle size can be readily assessed from the SEM.

In one embodiment, the method of manufacture includes the addition of carbon dioxide present inside the precipitation reactor to carbonate the calcium hydroxide in the precipitation reactor, i.e., to produce precipitated calcium carbonate in the precipitation reactor. Continuously supplying calcium hydroxide as fine droplets and/or particles to the contained gas.

Calcium hydroxide or other suitable source of Ca ⁺⁺ ions can be used as the reactive mineral material, from which carbon dioxide is used to form calcium carbonate. Typically, the calcium hydroxide is fed to the precipitation reactor as a calcium hydroxide sludge, i.e. calcium hydroxide dispersed in water such as milk of lime, but it can also be fed as a calcium hydroxide solution. The material is advantageously fed into the reactor via a disintegration and spray device located in or connected to the reactor.

In the above method, a so-called impact mixer type disintegration/spraying device can be used. In this type of mixer, very fine droplets and/or particles are formed from the calcium hydroxide sludge or solution.

In addition to the sludge of calcium hydroxide, a carbon dioxide-containing gas that produces sedimentation and is pure or nearly pure carbon dioxide, combustion gas, or other suitable gas containing _CO2 is fed to the sedimentation reactor. supplied continuously.

To produce the desired small particles, precipitation at a low reaction temperature of less than 65°C, typically 10-65°C, more typically 30-65°C, most typically less than 40°C. It is advantageous to generate

Aqueous dispersions of PCC particles have a dry matter content of about 5 to 50% by weight, in particular about 28 to 42% by weight, of the total weight of the dispersion.

In addition to providing an aqueous dispersion of PCC particles with an average size of about 30-60 nm as a starting material for the process, the primary PCC particles, typically size 2, within the average size range of 30-60 nm are provided. Aqueous dispersions with PCC agglomerates of ˜4 μm can also be provided. Such aggregates and aqueous dispersions containing such aggregates are disclosed in US Pat.

Thus, in one embodiment, the dispersion of talc and PCC particles in the aqueous phase comprises 50-95 parts by weight of platelet-shaped particles and 5-50 parts by weight of average size of about 2-40 μm, especially about 2.5. Precipitated calcium carbonate granules of ˜30 μm, preferably about 4-15 μm, obtained by dispersing with liberated primary particles of average diameter 30-60 nm with precipitated calcium carbonate granules.

In one embodiment, talc or similar platelet-like particles are placed in an aqueous dispersion of precipitated calcium carbonate particles (or agglomerates formed by such primary particles) with an average diameter of 30-60 nm in a zone of high shear. disperse to

In the context of the present invention, in the zone of high shear force the shear rate is typically in the range 1-10000 s ⁻¹ , typically in the range 10-1000 s ⁻¹ .

In one embodiment, the high shear zone is formed by one impact mixer or a cascade of impact mixers.

According to any of the above embodiments, dispersing talc in an aqueous atmosphere with nano-sized PCC particles results in a stable dispersion. In this dispersion, the precipitated calcium carbonate particles disperse the platelet-like molecules, in particular such that the platelet-like particles are at least partially separated from each other.

Surprisingly, dispersed talc particles "spaced" from other talc particles by PCC particles on one or several sides thereof form an efficient barrier when deposited as a layer on a substrate. was found to be possible. Typically, the thickness of such layers ranges from 0.1 to 100 μm, especially from about 1 to 10 μm.

To prepare a suitable coating composition, a dispersion of talc and PCC is mixed with a water-soluble or water-dispersible binder.

In one embodiment, a water-soluble or water-dispersible binder is added and mixed in the dispersion in an amount of 1 to 75% by weight, for example 15 to 65% by weight, particularly 20 to 60% by weight in terms of dry matter. .

In one embodiment, the binder is a polymer latex such as a styrene acrylate, acrylate or vinyl acetate acrylate latex, or mixtures thereof; water-soluble derivatives of starches, proteins, natural polymers such as carboxymethylcellulose or other cellulose derivatives; polyvinyl alcohol. or a mixture of two or more of said binders.

Typically, the binder is added to the aqueous dispersion in the form of an aqueous composition having a dry matter content of 30-70% by weight, in particular about 40-60% by weight.

The resulting dispersion with a dry matter content of 40 to 60% by weight, for example, generally has a Brookfield viscosity ( 100 rpm).

In one embodiment, the dispersion is free or substantially free of added thickening agents. It is particularly advantageous that the PCC component helps obtain the proper viscosity without the addition of conventional thickeners that can compromise barrier properties.

Based on the foregoing, one preferred embodiment is an aqueous composition of coating particles and a binder suitable for forming a dispersed barrier coating on a substrate, comprising:
- 50 to 95 parts by weight of platelet-shaped particles;
- 5 to 50 parts by weight of precipitated calcium carbonate particles with an average particle size of 30 to 60 nm,
It comprises an aqueous composition having a dry matter content of greater than 30% by weight, a Brookfield viscosity (100 rpm) of 300-2500 cP, and further comprising 1-75% by weight of a water-soluble binder on a dry matter basis.

One embodiment of the above coating composition comprises 40-60 parts by weight of talc, 20-30 parts by weight of precipitated calcium carbonate and 15-65% by weight, especially 20-60% by weight of a water-soluble binder on a dry matter basis. including. This composition exhibits a Brookfield viscosity (100 rpm) of 1000-2000 cP.

As noted above, the aqueous dispersions of the present invention can be used to form dispersed barrier coatings on substrates. In particular, the substrate to be coated is selected from the group of fibrous substrates, in particular porous fibrous substrates, for example substrates comprising cellulose fibers or lignocellulose fibers, or combinations thereof. Paper and cardboard sheets, webs and blanks are examples of particularly suitable substrates.

In one embodiment, the aqueous suspension is applied at 1-25 g/m ² , in particular 5-20 g/m ² , for example 5-15 g/m ² per side of the substrate.

The aqueous dispersion can be applied onto the substrate in the form of one or more overlapping layers.

The following non-limiting examples illustrate embodiments.

Example 1
An aqueous suspension was prepared by dispersing talc in an aqueous slurry of nano-sized PCC particles obtained as described in US Pat. The median particle size (d50) of the talc used was 3.0 μm and 34% by weight of the particles were smaller than 2 μm.

Thus, 75 parts by weight of talc were dispersed in an aqueous slurry of 25 parts by weight of nano-sized PCC particles using an ATREX mixer (an impact mixer capable of obtaining a high shear zone).

The dry matter content of the dispersion obtained was about 50%. The dispersion was very viscous. In addition, no sedimentation of solids was observed even after standing at room temperature (25° C.) for more than 30 days.

To prepare a suitable coating composition, a binder consisting of a synthetic styrene acrylate latex was added to the PCC dispersion in an amount of about 50 parts by weight solids. The dry matter content of the added latex was 50% by weight. Binders were added by mixing in a conventional blade mixer. The compositions thus obtained were also blended with conventional dispersing aids such as biocides. The dry matter content of the coating composition was about 50%.

Similar to the PCC dispersion, the coating composition was stable and no solids settled out of the composition after standing at room temperature for more than 30 days.

For comparison, a talc dispersion was also provided as a reference.

SEM analysis was performed. The results are shown in the attached SEM photographs.

As is clear from the SEM electrophotograph, the reference talc particles are densely packed. In contrast, in this test the talc particles are separated and located far apart from each other. Nano-sized PCC can be seen as a hazy material in the surface photograph.

A similar difference in the degree of loading of talc particles can be seen in the cross-sections. This study shows that nano-sized PCC can be found in the surface structure mixed with the binder.

The coating compositions were utilized for the following coating experiments.

Example 2
Three pilot coating trials were conducted. Two of the tests were performed on precoated LWC basepaper and one on precoated paperboard.

The resulting WBBC paper/board was subjected to barrier analysis for KIT, oxygen, water vapor, grease, and oil barriers.

Tables 1-3 below show the test design, the resulting coating paste quality and the measured barrier values.

As is evident from the results presented in the table, water-based barrier coatings using novel mixtures of conventional platelet minerals and nano-sized _CaCO3 -based pigments have a higher oxygen content than WBBC containing conventional platelet minerals. and improved water vapor barrier and maintained KIT, grease and oil barrier.

Also, pilot coater runnability was found to be better with the new pigment mixture compared to WBBC containing pure conventional platelet minerals.

Without wishing to be bound by any particular theory, it is believed that one of the reasons for the improved barrier properties of the new pigment mixture is due to a more closed coating surface structure and an intricate pigment particle network. Seem. This can be seen from the attached SEM image.

The coating dispersions of the present invention can be used to obtain barrier coatings with improved gas barrier properties, especially oxygen barrier properties, on any substrate. This aqueous dispersion can also be used to obtain barrier coatings with improved mineral oil barrier properties on substrates.

Food packages and packaging are applications of particular interest.

Claims (18)

A stable aqueous dispersion of platelet-shaped particles and precipitated calcium carbonate comprising:
- 50 to 95 parts by weight of platelet-shaped particles;
- 5 to 50 parts by weight of precipitated calcium carbonate particles with an average diameter of 30 to 60 nm,
the dry matter content is greater than 30% by weight and the Brookfield viscosity (100 rpm) is between 200 and 5000 cP;
Said platelet-like particles are typically in the range of 1-10000 s-1 with 5-50 parts by weight of precipitated calcium carbonate particles with an average particle size of 30-60 nm in an aqueous phase. is an aqueous dispersion obtained by dispersing in a dispersing zone at a shear rate between 10 and 1000 s-1 . 2. The dispersion as claimed in claim 1, comprising 60 to 85 parts by weight, especially 70 to 80 parts by weight of platelet-shaped particles and 15 to 40 parts by weight, especially 18 to 28 parts by weight of precipitated calcium carbonate particles. 3. The dispersion of claim 1 or 2, wherein the platelet-shaped particles are selected from the group of talc, kaolin, bentonite and combinations thereof. 50-95 parts by weight of platelet-shaped particles in an aqueous phase together with 5-50 parts by weight of precipitated calcium carbonate particles with an average particle size of 30-60 nm in the range of 1-10000 s-1, typically 10-1000 s-1. A dispersion according to any one of claims 1 to 3, obtained by dispersing in a zone of high shear force at a shear rate of between 1. 50 to 95 parts by weight of platelet-shaped particles in an aqueous phase, 5 to 50 parts by weight of precipitated calcium carbonate granules having an average size of about 2 to 40 μm, especially about 2.5 to 30 μm, preferably about 4 to 15 μm. obtained by dispersing with precipitated calcium carbonate granules capable of liberating primary particles with an average diameter of 30-60 nm when subjected to shear forces in an aqueous dispersion. 3. Dispersion according to item. 6. A dispersion according to claim 4 or 5, wherein the zone of high shear force is formed by one impact mixer or a cascade of impact mixers. Dispersion according to any one of the preceding claims, wherein the precipitated calcium carbonate particles disperse the platelet-shaped molecules, in particular such that the platelet-shaped particles are at least partially separated from each other. 1 to 75% by weight, for example 15 to 65% by weight, especially 20 to 60% by weight of a water-soluble or water-dispersible binder in terms of dry matter,
Said binders are preferably polymeric latices such as styrene acrylate, acrylate or vinyl acetate acrylate latices, or mixtures thereof; water-soluble derivatives of starches, proteins, natural polymers such as carboxymethylcellulose or other cellulose derivatives; A dispersion according to any one of claims 1 to 7, selected from synthetic polymers; or mixtures of two or more thereof. A binder is added to the aqueous dispersion formed by the platelet-shaped particles and the precipitated calcium carbonate particles, in particular the binder has a dry matter content of 30 to 70% by weight, especially about 40 to 60% by weight. 9. The dispersion of claim 8, which is added to the aqueous dispersion in the form of Less than 5% by weight, preferably less than 1% by weight of suspended solids settle when left at 10°C to 50°C for 30 days, the dispersion being free of or substantially free of added thickening agents. The dispersion according to any one of claims 1 to 9, which does not contain in Dispersion according to any one of the preceding claims, wherein the dry matter content is 40-60% by weight and the Brookfield viscosity (100 rpm) is 300-2500 cP, in particular 500-2000 cP. - 50 to 95 parts by weight of platelet-shaped particles;
- an aqueous dispersion having a dry matter content of more than 30 wt. and
50-95 parts by weight of platelet-shaped particles in an aqueous phase together with 5-50 parts by weight of precipitated calcium carbonate particles with an average particle size of 30-60 nm in the range of 1-10000 s-1, typically 10-1000 s-1. dispersing in a dispersing zone at a shear rate of between 1;
A method for making a stable aqueous dispersion of platelet-shaped particles and precipitated calcium carbonate, comprising: 13. The step of dispersing 50 to 95 parts by weight of platelet-shaped particles in an aqueous phase with 5 to 50 parts by weight of precipitated calcium carbonate particles with an average particle size of 30 to 60 nm in a zone of high shear. the method of. 50 to 95 parts by weight of platelet-shaped particles in an aqueous phase, 5 to 50 parts by weight of precipitated calcium carbonate granules having an average size of about 2 to 40 μm, especially about 2.5 to 30 μm, preferably about 4 to 15 μm. 14. The method of claim 12 or 13, comprising dispersing with precipitated calcium carbonate granules, which are capable of liberating primary particles of average diameter 30-60 nm when subjected to shear forces in aqueous dispersion. A method according to any one of claims 12 to 14, wherein the zone of high shear force is formed by one impact mixer or a cascade of impact mixers. Use of an aqueous dispersion according to any one of claims 1 to 11 for forming a dispersed barrier coating on a substrate,
said aqueous dispersion is applied onto a substrate in the form of one or more overlapping layers,
Said substrate is preferably selected from the group of fibrous substrates, in particular porous fibrous substrates, e.g. substrates comprising cellulose fibers or lignocellulose fibers, or combinations thereof,
Use of aqueous dispersions. Said aqueous dispersions are used to obtain barrier coatings on substrates with improved gas barrier properties, in particular oxygen barrier properties, or to obtain barrier coatings with improved mineral oil barrier properties on substrates. Use according to claim 16, for use. Use according to claim 16 or 17, wherein the aqueous suspension is applied to the substrate at 1-25 g/m2, in particular 5-20 g/m2, for example 5-15 g/m2 per substrate side.

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